Android Tutorial

Android Tutorial 307

public void deleteBooksByAuthor(Integer authorID) {

int numBooksDeleted = mDatabase.delete(“tbl_books”,

“authorid=?”, new String[] { authorID.toString() });

}

Working with Transactions

Often you have multiple database operations you want to happen

all together or not at all. You can use SQL Transactions to group

operations together; if any of the operations fails, you can handle

the error and either recover or roll back all operations. If the

operations all succeed, you can then commit them. Here we have

the basic structure for a transaction:

mDatabase.beginTransaction();
try {
// Insert some records, updated others, delete a few
// Do whatever you need to do as a unit, then commit it
mDatabase.setTransactionSuccessful();
} catch (Exception e) {
// Transaction failed. Failed! Do something here.
// It‟s up to you.
} finally {
mDatabase.endTransaction();
}

Now let’s look at the transaction in a bit more detail. A transaction

always begins with a call to beginTransaction() method and a

try/catch block. If your operations are successful, you can commit

your changes with a call to the setTransactionSuccessful() method.

If you do not call this method, all your operations are rolled back

and not committed. Finally, you end your transaction by calling

endTransaction(). It’s as simple as that.

In some cases, you might recover from an exception and continue

with the transaction. For example, if you have an exception for a